Bis-quaternary ammonium compounds which exhibit antimicrobial activities against bacteria, fungi and the like are known for many years, and are still used widely as antimicrobial agents at present. The currently-employed, antimicrobial bis-quaternary ammonium compounds are generally excellent in antimicrobial activities, but at the same time, biodegradation products of these compounds have high residual toxicity. Concerning the actual use of these compounds, they involve problems in the safety to the environment and the solubility and safety to water so that a limitation is imposed on the applicable range thereof. Further, the conventional bis-quaternary ammonium compounds are also accompanied by drawbacks in that their antimicrobial power is competed with saccharides, proteins, lipids and the like; their antimicrobial power is lowered in a low pH (acidic) range, and they are not effective against microbial endospores.
Accordingly, there have been reported bis-quaternary ammonium compounds represented by the following formula (A) or (B) (Patent Document 1):
wherein Y represents a substituted or unsubstituted pyridine ring, quinoline ring, isoquinoline ring or thiazoline ring, R1 represents a substituted or unsubstituted alkylene group or alkenylene group having 2 to 10 carbon atoms, R2 represents a substituted or unsubstituted alkyl group having 6 to 18 carbon atoms and bonded to the nitrogen atom of Y, and X represents an anion;
bis-quaternary ammonium compounds represented by the following formula (C) (Patent Document 2):
wherein Z represents a pyridine ring, R1 and R2 may be the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, R3 represents an alkenylene group having 3 to 18 carbon atoms, R4 represents an alkyl or alkenyl group having 6 to 18 carbon atoms and bonded to the ring nitrogen atom of Z, and X represents an anion; and
bis-quaternary ammonium compounds represented by the following formula (D) (Patent Document 3):
wherein Z represents a substituted or unsubstituted pyridine ring or quinoline ring, R3 represents a substituted or unsubstituted alkylene or alkenylene group having 2 to 18 carbon atoms, R4 represents a substituted or unsubstituted alkyl group having 6 to 18 carbon atoms and bonded to the nitrogen atom of Z, R1 and R2 may be the same or different and each represents an alkyl group having 1 to 3 carbon atoms, hydroxyl group, amino group, alkoxy group having 1 to 3 carbon atoms or hydrogen atom bonded to an atom in Z other than said nitrogen atom, and X represents an anion.    Patent Document 1: JP-A-8-301703    Patent Document 2: JP-A-10-095773    Patent Document 3: JP-A-6-321902